1. Field of the Invention
The present invention relates to a high frequency module used in a communications apparatus for a wireless local area network (LAN).
2. Description of the Related Art
Attention has been recently drawn to a wireless LAN that forms a LAN through the use of radio waves as a technique for constructing a network easily. A plurality of standards are provided for the wireless LAN, such as the IEEE 802.11b that uses a 2.4 GHz band as a frequency band and the IEEE 802.11a and the IEEE 802.11g that use a 5 GHz band as a frequency band. It is therefore required that communications apparatuses used for the wireless LAN conform to a plurality of standards.
Furthermore, the communications status on the wireless LAN varies depending on the location of the communications apparatus and the environment. It is therefore desirable to adopt a diversity for choosing one of a plurality of antennas whose communications status is best.
In the communications apparatus for the wireless LAN, a circuit portion (hereinafter called a high frequency circuit section) that is connected to antennas and processes high frequency signals is incorporated in a card-shaped adapter, for example. In addition, it is expected that the communications apparatus for the wireless LAN is installed in a mobile communications device such as a cellular phone. A reduction in size of the high frequency circuit section is therefore desired.
A type of mobile communications device such as a cellular phone is known, wherein a high frequency circuit section is formed as a module operable in a plurality of frequency bands. For example, the Published Unexamined Japanese Patent Application (hereinafter referred to as “JP-A”) 2003-152588 discloses a module incorporating two diplexers and a single switch circuit. In this module, the switch circuit switches one of the two diplexers to be connected to the single antenna. Each of the diplexers separates two signals in different frequency bands from each other.
JP-A 2003-37520 discloses a high frequency switch provided for a diversity that enables a transmission port and a reception port to be each switched to be connected to one of two antennas.
Each of JP-A 2001-136045 and JP-A 2001-119209 discloses a module incorporating a duplexer for separating transmission signals from reception signals. This module incorporates two band-pass filters each of which is made up of inductor conductors and capacitor conductors of a layered structure made up of a plurality of insulating layers, a plurality of inductor conductors and a plurality of capacitor conductors. Furthermore, these two publications disclose a technique in which the axis of the inductor conductors making up one of the band-pass filters is made orthogonal to the axis of the inductor conductors making up the other of the band-pass filters. In addition, the two publications disclose a diplexer as another example of the module to which the above-mentioned technique is applied. These publications disclose that the diplexer is formed by using a combination of a low-pass filter and a high-pass filter, for example.
As described above, it is desirable that the communications apparatus for the wireless LAN conforms to a plurality of standards whose operable frequency bands are different. It is therefore desired that the high frequency circuit section of the communications apparatus for the wireless LAN is capable of processing transmission signals and reception signals in a plurality of frequency bands. In addition, it is preferred that the communications apparatus for the wireless LAN adopts a diversity. Because of this, the high frequency circuit section of the communications apparatus for the wireless LAN preferably has a function of switching a plurality of antennas to be connected to an output port of reception signals and an input port of transmission signals. Furthermore, a reduction in size of the high frequency circuit section of the communications apparatus for the wireless LAN is desired.